Inhaled nitric oxide in moderate-to-severe COVID-19 acute respiratory distress syndrome: a retrospective cohort study

OBJECTIVE
In this study, we present the findings from a cohort of patients with COVID-19 with acute respiratory distress syndrome who underwent standard therapy, including prone positioning, with or without adjunctive inhalation of nitric oxide. Our investigation sought to determine whether inhaled nitric oxide administration yielded clinical enhancement in this population. Remarkably, nitric oxide administration elevated the PaO2/FiO2 ratio, which is indicative of improved oxygenation. Despite this improvement, discernible mortality benefits did not emerge in association with the inhaled nitric oxide treatment. To evaluate the responsiveness of COVID-19 acute respiratory distress syndrome patients to inhaled nitric oxide as part of their standard therapy.


METHODS
This retrospective cohort study included critically ill adult patients with confirmed COVID-19 treated between March 2020 and May 2021. Eligible patients with moderate-to-severe acute respiratory distress syndrome due to COVID-19 were subsequently categorized into two groups based on inhaled nitric oxide use throughout their stay in the intensive care unit. The primary endpoints were overall mortality and improvement in oxygenation parameters 6 hours after inhaled nitric oxide use.


RESULTS
A total of 481 patients admitted to the intensive care unit due to COVID-19 acute respiratory distress syndrome were screened, 105 of which were included. Among the 105 patients, inhaled nitric oxide therapy was used in 33 patients, will 72 did not undergo inhaled nitric oxide therapy. No significant difference in mortality was observed between the groups (67% for the treatment and 82% for the no-treatment groups respectively, p=0.173). Among the patients who used inhaled nitric oxide, 17 (51%) were considered responsive to therapy. There was no significant difference in the length of stay in the intensive care unit (p=0.324) or total hospitalization time (p=0.344).


CONCLUSION
Inhaled nitric oxide rescue therapy improved oxygenation in patients with COVID-19 with moderate-to-severe acute respiratory distress syndrome but did not affect mortality.


Inhaled nitric oxide in moderate-to-severe COVID-19 acute respiratory distress syndrome: a retrospective cohort study ❚ Highlights
۪ Acute respiratory distress syndrome is a severe presentation of COVID-19 without effective treatment despite intensive research.
۪ Inhaled nitric oxide is a vasodilator that has been studied in patients with acute respiratory distress syndrome COVID-19 yielding contradictory results.
۪ The use of inhaled nitric oxide rescue therapy in critically ill patients with COVID-19 experiencing moderate-to-severe acute respiratory distress syndrome was significantly associated with an improvement in oxygenation parameters with no difference in mortality.

❚ INTRODUCTION
Acute respiratory distress syndrome (ARDS) is a severe presentation of COVID-19, the disease caused by SARS-CoV-2. (1)Despite intensive research, some treatments have demonstrated certain effects, although none can be considered excellent for treating COVID-19-induced ARDS. (2)uring this pandemic, intensive research was conducted to identify therapeutic options.Among the studied medications is nitric oxide (NO), an endogenous signaling molecule that can be inhaled. A meta-analysis published by Cochrane in 2016 showed an improvement in the PaO 2 /FiO 2 ratio in ARDS of any cause with iNO, although no impact on mortality was observed. (4)ince the advent of COVID-19, NO has emerged as a potential therapeutic target.Physiologically, NO has bronchodilatory, antithrombotic, and arterial vasodilatory effects. (5)Akaberi et al. (6) showed that NO, in vitro, also has an anti-replicative effect against SARS-CoV-2.Therefore, NO was proposed to potentially improve oxygenation and outcomes in critically ill patients with ARDS arising from COVID-19.
There are few publications on the effectiveness of iNO in the treatment of ARDS caused by COVID-19, and they have controversial results.Two series of cases with a small number of patients showed little response to this therapy. (7,8)Contrary to these findings, one clinical trial and one retrospective cohort of 71 patients reported a response rate of approximately two-thirds when considered improvement by >20% in terms of the PaO 2 /FiO 2 ratio. (9,10)Recently, a multicenter cohort study with an iNO Group of 76 patients found an improvement in oxygenation parameters; however, there was no difference in mortality rates. (11)In addition, a recent meta-analysis that included eight studies and 265 patients found an improvement in oxygenation parameters in 66% of the patients, but without benefits to the mortality rate. (12)he combined use of iNO with other pulmonary vasoactive agents, such as almitrine, has been studied.Almitrine has been reported to elevate oxygenation in patients with ARDS owing to its hypoxic pulmonary vasoconstriction action.15)(16) This study is an observational retrospective medical chart review conducted at a public COVID-19 reference center in São Paulo, where iNO was used as a rescue therapy in a group of mechanically ventilated patients with moderate-to-severe COVID-19 ARDS.We hypothesized that iNO could improve oxygenation parameters and reduce mortality in patients with COVID-19 and ARDS.

❚ OBJECTIVE
To evaluate the responsiveness of COVID-19 acute respiratory distress syndrome patients to inhaled nitric oxide as part of their standard therapy.We compared all-cause mortality and the duration of mechanical ventilation between patients who inhaled or did not inhale nitric oxide.

❚ METHODS
This study was conducted in accordance with the Declaration of Helsinki.The requirement for informed consent was waived by the Research Ethics Committee of Hospital Israelita Albert Einstein owing to the retrospective, non-interventional nature of the study and anonymized data analysis.The study was approved under the registration numbers (CAAE: 53009721.0.0000.0071;#5.200.505.Data analysis was conducted in an aggregated manner so that the secrecy and privacy of the data were respected throughout the process.

Study design
This study was a retrospective medical chart review conducted at a single center, a public hospital that served as a reference for the treatment of COVID-19 in São Paulo, Brazil, during the pandemic.The period analyzed was from March 2020 to May 2021.

Inclusion and exclusion criteria
Adult patients aged >18 years with a COVID-19 diagnosis and admitted to the intensive care unit (ICU) were screened for enrollment.All patients under mechanical ventilation for moderate-to-severe COVID-19 ARDS and who were placed in the prone position and/or received iNO were included.
Patients with no confirmed diagnosis of COVID-19 or those who did not require mechanical ventilation were excluded.Patients admitted to the ICU for reasons other than ARDS, and those with incomplete information in their medical records were excluded.In this study ARDS was defined according to the American-European Consensus Conference (AECC), (17,18) and COVID-19 was considered the cause when confirmed by RT-PCR.

Intervention
As standard institutional therapy, all patients were ventilated under protective parameters for 6 hours, and the PaO 2 /FiO 2 ratio was measured.If the ratio was <200, a PEEP titration was performed, and 2 hours later, a new blood gas analysis was performed.If the PaO 2 /FiO 2 ratio was <150 after PEEP titration, the prone position was indicated, and the ratio was evaluated 4 hours later.Patients who evolved with an increase of PaO 2 /FiO 2 ≥20 after the prone position were maintained in the position for 16 to 20 hours were considered responsive to therapy.Those who did not present with an increase in PaO 2 /FiO 2 ≥20 were considered not responsive and were treated with alveolar recruitment in the prone position.In cases where there was no response to the prone position or when it could not be applied, iNO was considered as a rescue therapy.Inhaled NO was administered for a minimum period of 6 hours until ventilatory improvement was achieved, which was measured using the PaO 2 /FiO 2 ratio.We utilized the iNO dose institutionally applied in clinical practice (20 einstein (São Paulo).2024;22:1-6 parts per million), and the gas was reduced or suspended based on signs of toxicity or suspicion thereof.
We analyzed PaO 2 /FiO 2 before and after prone positioning, as well as with iNO therapy.2,13) All patients received dexamethasone as standard glucocorticoid therapy, and there were no additional medications intended to treat COVID-19.Other medications such as sedatives, neuromuscular blockers, inotropes, vasoconstrictors, antibiotics, anticoagulants, and antiarrhythmics were used according to the patient's clinical needs.

Data collection
Demographics, clinical data, and complementary examinations were collected from all the patients included in the study.The patients were divided into two groups: with and without iNO therapy.These groups were matched by age, sex, PaO 2 /FiO 2 ratio, and comorbidities.2,13) The primary endpoints analyzed were responsiveness to iNO and all-cause mortality during ICU stay.The secondary endpoints were the time of mechanical ventilation and length of ICU stay.

Statistical analysis
Data were described as mean, standard deviation, minimum, maximum, median, and quartiles for quantitative variables.Frequency tables were used for the qualitative variables.To compare the clinical outcomes between the groups, the χ 2 or Fisher's exact test and Student's t-test or-the Mann-Whitney test were used, depending on the characteristics of the distribution.
Non-parametric Kaplan-Meier analyses were performed to estimate the overall survival of patients in the ICU and after application of the prone position and iNO treatment.The log-rank test was used to compare the treatment survival curves.Patient survival was censored based on the date of ICU discharge.
The normality of the variables was checked using the Shapiro-Wilk test.The significance level adopted in these analyses was set at 5%.A power test was performed, and the results are presented in a table.Analyses were performed using R software, version 4.1.1.

❚ RESULTS
A total of 481 patients with COVID-19 and ARDS admitted to the ICU were screened for enrollment, and 105 were included in the study.The patients were divided into two groups: patients who received iNO therapy (33) and those who did not (72) (Figure 1).The baseline characteristics of the individuals were male predominance (60%) and a median age of 56 years.The main comorbidities in overall patients were hypertension, diabetes mellitus and obesity.Alcohol consumption differed between groups (p=0.014;Table 1).The responsiveness to the prone position was higher in the group that did not use iNO (p=0.005,power=0.999).In addition, the PaO 2 /FiO 2 ratio after prone positioning was higher in the group without iNO (p=0.008,power=0.890;Table 2).There were no differences between the groups regarding the other patterns of intensive support care (Table 3).
The median survival of the group without iNO was 20 days (95% confidence interval (95%CI) =7 -missing value days), whereas that of patients in the iNO Group was 23 days (95%CI=19 -27 days).

❚ DISCUSSION
We studied a cohort of patients with COVID-19induced ARDS treated with standard therapy, including those in the prone position with or without iNO.We hypothesized that iNO would improve oxygenation parameters and reduce mortality rates in these patients.We did not observe a mortality benefit despite 51% of the patients in this using iNO showing improved PaO 2 /FiO 2 ratios.
Literature on the use of iNO in ARDS caused by COVID-19 is still scarce, but previous studies have shown similar responsiveness to iNO.For instance, Abou-Arab et al. (9) conducted a clinical trial involving 34 patients and reported a response rate of 65%.Abman et al. (10) reported a response rate of 62% in a retrospective cohort of 37 patients treated with iNO.In a recent meta-analysis, Alqahtani et al. (12) observed an overall response rate of 66% among the seven studies  The primary endpoints were iNO responsiveness and overall mortality during the ICU stay.There was no significant difference in the overall mortality between the groups (p=0.173,power=0.891;Table 4 and Figure 2).Of the 33 patients who received iNO, 9 had not previously undergone prone positioning due to contraindications such as hemodynamic instability and body mass index over 40kg/m 2 .Among patients who used iNO, 17 (51%) were considered responsive to therapy.Regarding secondary outcomes, we did not observe differences in mechanical ventilation time (p=0.383),ICU length of stay (p=0.324), or total hospitalization time (p=0.344;Table 4).included but with considerable heterogeneity between the results of the studies analyzed.In fact, not only is responsiveness to iNO controversial among the few reports, but so is the methodology used.While Abou-Arab et al. (9) used NO before indicating pronation and only performed pronation if there was no response, we used NO as a rescue therapy.Furthermore, Abman et al. (10) used iNO in patients with a PaO 2 /FiO 2 ratio between 100 and 300, which represents a less severe spectrum of ARDS than that observed in our study population with moderateto-severe levels.
Another recent multicenter cohort study included 815 patients and evaluated the use of iNO in 76 of them.In agreement with most previous reports, including ours, they observed an improvement in oxygenation parameters but without a difference in mortality rates. (11)onsidering adverse effects with the iNO use, Al Sulaiman et al. (11) described a higher incidence of acute kidney injury, pneumonia and acute liver injury associated with the use of iNO.No differences in renal impairment or dialysis indications were observed between the groups.
Despite a 51% response rate to iNO in our cohort, we did not observe any mortality benefits.These results are similar to those of previous studies, but they should be interpreted with caution because of the non-randomized design of the study.Although we followed a similar methodological design as in previous observational trials, we believe that the retrospective and non-randomized nature of the study may have interfered with the measurement of the effects of iNO.In our sample, NO was used in the most severe and refractory patients in the prone position as a rescue therapy.As a result, we believe that there was a selection bias, which we were able to identify when a significant difference was found in the post-prone PaO 2 /FiO 2 ratio between the groups, suggesting worse basal oxygenation in the iNO Group.The design of a randomized clinical trial with matched control and treatment groups should follow as the next step in further studies.

❚ LIMITATIONS
This study had several limitations.First, this was a retrospective observational study; therefore, there was no planned design for the matched groups.Secondly, the sample size was small.Finally, we were unable to eliminate the selection bias of the most severely ill patients receiving iNO therapy, which could have minimized a possible unmeasured effect.However, this was a hypothesis-generating study, and randomized clinical trials can provide stronger evidence.

❚ CONCLUSION
We conclude that inhaled nitric oxide rescue therapy in COVID-19 patients with moderate-to-severe acute respiratory distress syndrome is associated with an augmentation in oxygenation with no mortality benefits.Neither mechanical ventilation nor intensive care unit length of stay were altered as a result of inhaled nitric oxide therapy.Further randomized clinical studies are necessary to confirm these findings.
undergo prone positioning 131 did not undergo endotracheal intubation 19 ICU admission for reason other than COVID-19 31 had missing data ICU: intensive care unit.

Figure 1 .
Figure 1.Recruitment process of COVID-19 patients screened for eligibility

Figure 2 .
Figure 2. Survival analysis comparison between groups without and with inhaled nitric oxide therapy

Table 1 .
Demographics and baseline characteristics of the groups without and with inhaled nitrogen oxide therapy Values are presented as median [interquartile range] or n (%).χ 2 test (significance level was 5%).COPD: chronic obstructive pulmonary disease; iNO: inhaled nitric oxide.

Table 3 .
Intensive care support for groups without and with inhaled nitric oxide therapy

Table 4 .
Patient outcomes for patients with COVID-19 induced acute respiratory distress syndrome who received and did not receive inhaled nitric oxide therapy einstein (São Paulo).2024;22:1-6